Mark,
I am going to be critical of your e-mail. I hope you take it as constructive criticism.
"Normally the organic acid is decomposed when exposed to reflow or wave solder temperatures. "
-I will be picky here and say that it either reacts with the oxide on the metal surface, reacts with/dissolves the OSP or it sublimes away.
"It then forms the whitish film that is difficult to remove with any solvent."
- Very rarely have I seen a significant white film UNLESS someone has tried to clean a low residue flux that is not compatible with IPA and/or the water that condenses as the IPA evaporates and lowers the board/flux surface below the dew point. I agree the tin salts that form the white residue are difficult to impossible to remove.
"However, if the flux is not heated to destruction, such as flux used in touch-up that is flooded onto the PWB, and then not heated sufficiently by the soldering iron it remains active. It is an acid and will cause corrosion, but even more it will allow current flow. It is hygroscopic and absorbs water from the air. It will then ionize."
- What do you mean by "active"? All the low residue fluxes that claim to be no-clean that I have ever used that have passed copper mirror, halide ion, SIR and electrochemical migration are only "active" once they are heated. At room temperature you are so far in the valley from the activation energy barrier that they are not going to do anything. And I can't believe that all the thousands of SIR and ECM coupons I have run over the last 20 years have had all the carboxylic acids removed/destroyed/sublimed away, which means that some was left and they have not allowed current flow of any magnitude, if at all.
"Active no-clean flux residues are crystalline in form"
- Maybe. It depends on what else is left with the carboxylic acids, speed of reaction and the reaction products. I would expect a good portion of the residues to be amorphous.
"and will easily dissolve in the appropriate solvent, usually water or IPA depending on the type of flux used."
- Crystallinity does not equal easy dissolution. Quartz crystals only dissolve in things like HF. And if all these residues easily dissolved in the solvents you mention, we would not even be having this discussion.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Woolley, Mark D. (Mark)
Sent: Friday, September 10, 2010 10:04 AM
To: [log in to unmask]
Subject: Re: [TN] Cleaning No Clean Flux
No-clean flux usually has an organic acid in it as its active compound.
Normally the organic acid is decomposed when exposed to reflow or wave
solder temperatures. It then forms the whitish film that is diffidult
to remove with any solvent. However, if the flux is not heated to
destruction, such as flux used in touch-up that is flooded onto the PWB,
and then not heated sufficiently by the soldering iron it remains
active. It is an acid and will cause corrosion, but even more it will
allow current flow. It is hygroscopic and absorbs water from the air.
It will then ionize.
Active no-clean flux residues are crystalline in form and will easily
dissolve in the appropriate solvent, usually water or IPA depending on
the type of flux used.
mark
mark
Mark Woolley |PTRL Laboratory | Avaya | 1300 West 120th Ave |
Westminster, CO 80234 USA |
Voice (Lab): (303) 538-2166 | email: [log in to unmask] |
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rick Bell
Sent: Friday, September 10, 2010 7:57 AM
To: [log in to unmask]
Subject: Re: [TN] Cleaning No Clean Flux
----------------------
[quote]
"Also, why would "No cleans" need cleaning?"
----------------------
I'm willing to bet someone's chair that the most common answer is
"...because our customer requested it." That's true in our case,
anyway.
We use a chemistry from Kyzen. IPA isn't capable for our process
materials. You'd probably have to verify for yourself if it works for
you.
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert DeQuattro
Sent: Friday, September 10, 2010 8:41 AM
To: [log in to unmask]
Subject: [TN] Cleaning No Clean Flux
Hello Everyone. I know there has been a lot of interesting dialogue the
past few days reference hand solder and flux and cleaning. My question
is "is isopropyl alcohol acceptable to use to clean no clean flux"? We
have Novec flux remover, but that leaves a white residue similar to what
some of you have complained about during the course of the related
thread. Any ideas on the best way to remove or avoid this. Also, why
would "No cleans" need cleaning?
Thanks,
Bob DeQuattro
Quality Manager
VR Industries, Inc
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